Frequency sensitive visual indicator



Oct. 22, 1957 R. L. CARNINE 2,810,883

FREQUENCY SENSITIVE VISUAL INDICATOR Filed April 18. 1955 .L I -4 aleVAL INPUT I 2 5 1: i E I CONDUCT! l/E 61145-5 ATTORNEY 2,810,883FREQUENCY SENSITIVE VISUAL INDICATOR -Robert Lscarnineywashington', D.C.', as'signor' to Ray- -=mond -M.-'WilInotte, Inca WashingtonyD. C., acor- --poration oif Mary-landv phois may be dispersed in asoli'd orliquid dielectric carrier, or may be disposed on a support independentlyofany carrier, in either ever'ifconstituting an electro- I"luminous'rnedium. The medium may be sandwiched between a pair ofelectrodes, one of whichi'nay be transparent, and then constitutes thedielectric of an electrical cond'ens'er, which is luminous in responsetotheapplica- --tionthereto of timevaryingfvoltages. Such a-eondenserhas been'described in the U. S. Patent to E. L. Mager, No. 2,624,857, towhich reference is'niade for further detailedinformation as topreferredstructural' arrange- Inents.

In accordance with 'the'present'invcntion, in its preferred form,'atransparentelectrically conductive plate is utilized as-a support" fora mass of electroluminescent phosphor, which 'is embeddedin ai'highresistance solid dielectric carrier. A 'signalinput terminalisconnectedin par'allel to-corresponding' terminals ofia series of piezoelectriccrystals, the emainingterminals of which are coriiiected with'contactslocated at discrete points of the phosphor. Eachpiezo-electric. crystal is" fabricated to be 'seriesresonant to a'diiferen't frequency within a freq'uenc'y band. Iffde'sire'd', theselectivity curves" of the separatepiezoelectric crystals may o ierlapsu'fliciently that atleastone piezo-electric' crystal of the pluralityemployed is responsive to every "frequency within=the bandf It is then-acharacteristic of each 'piezo-electric crystal-that in response to afrequency towhic'hit is resonantit constitutescssentiallyashortcircuit', while in} esponse to other frequenciesit constitutes anopen circuit; The separatepiezo electric crystals accordinglyapplysignals'at differentfrequencies to' di'flerent points ofthe layerof electroluminescent phosphon-the signals passing through th e phosphorand viaa'tunilig indu'ctance to ground. A plurality ofelectroluminescent condensers are therebyformed, each one consisting'of(1) one of the contacts which proceed from the array of piezo-electriccrystals,- (2:) the area of the transparenttelectrically conductingplatewhich immediately-mnderlies the* 'cont-act, and-(3 thephosphor in itshigh resistance, high dielect'ric constant'medium. The tuningcoih 'whichis comrhon to all the electroluminescent condensers, resonates theindividual condensers to the frequency of the band under examination. Itis possible to accomplish this by means of a single coil, provided theband of frequencies is not unduly great, because the Q of the coil andits associated condenser or condensers is relatively low, of the orderof 20 or 30, while the Q of the associated piezo-electric crystals is ofthe order of 10,000 or 10,000,000.

It is well known that piezo-electric crystals are series resonant notonly to their fundamental frequencies, but also to harmonics of thesefrequencies. By virtue of the fact that the condenser and tuning coil inseries with United States PatenfO "ice 2,810,883 Patented Oct ZZ, 1957each piezo-electric crystal is a series'resonant circuit,- it

can in fact be resonant to only a single bandof frein-terms of voltageacross the electroluminescent co'ndenser. For that frequency to whichthe electroluminescent condenser and its associated tuning coil isresonant aresonant rise of voltage takes place across-the coridenser,the resonant rise'bei'ngof the order of '20 o r;30.

Since electroluminescent phosphors require a: minimum voltage for firingthe response of the systemtoharmonic frequencies at considerableamplitude may be completely eliminated, while the response of the systemto :relatively small amplitudes within a desired-band may beconsiderable.

: It isaccordingly a broad object of the'pr ese'ntrinvention toprovide anovelelectroluminescent indicator, in

which indications are produced at discrete points of anelectroluminescent medium in response to signals of discretefrequencies, and in which responses of the system to frequenciesharmonically-related to a desired band of frequencies are eliminated.

. It is a-more specific object of the presentinventio'n to provide asystememploying a'plurality of piezoelectric, crystals asfrequencyseparating devices, separate frequencies'being applied to discreteportions of. an electroluminescent medium, and the electroluminescent:mediumbeing tuned to a preselected band of; frequencies,

tothe practical exclusion offrequencies falling outside the" preselectedband.

The above and still'further features, objects, andi advantages oftheinvention will become apparcnt upon consideration of the followingdetailed description. of a specific embodiment oftheinvention,-especiallysyvlien taken in conjun'ction with the accompanyingdrawings, wherein the single figureof the drawings is-aschema'ticcircuit diagram of a system in accordance with'the pres ent, invention.40

Referring now more specifically to the accompanying drawings,thereference numeral '1 represents a'ftsig'nal input terminal to whichmay beapplied signalsderivin'g fromany source, such as from theintermediate-frequency amplifier of a radio receiver,-'a sonar'receiver;or the like, the band of frequencies being applied iniparallel to theinput terminals 2, 3, 4, of an array of*:piezo electric crystals 6;7, 8,The output electrodesl10, 1-1, 12, of the'piezo-electric crystals 6, 7,8,' respectively, are connected with or utilized asl'contacts, eachdirected to a different discretepoint of alayer M of electroluminescentphosphor. This phosphor may: be laid ona layer of dielectric material,or may befinc'orporat'ed thereinin-accordance with the teachings: of UlS'. Patent to.E. L Mager-2,654,857. The l'ayero'fphosphor maybesupportedon a sheet of electrically conductive glass 15, or other" transparentmaterial, the reference 'le denoting a conductive coating on theglasstpla'te ISiE Th'e conductive layer'l6 is connected via a tuning"coil1 7to a1 l qund01other rcferencepointq 11 Thepiezoclectric crystals6, 7, 8, inclusive, there being three such crystals illustrated 'for thesake of example only, and not by Way of limitation, may each be resonantto a different frequency, and the frequencies may be adjacent to oneanother, so that at least one of the crystals will be resonant to anyfrequency within a predetermined frequency band, ft to f2, which may beapplied to the terminal 1. Accordingly, for any frequency falling withinthe predetermined band, an alternating current will appear at one of theoutput terminals 10, 11, 12, Each of the contacts 10 to 12, inconjunction with that portion of the conductive layer 16 whichimmediately underlies it, represents a condenser having as itsdielectric medium a portion of the electroluminescent layer 14. Thiscondenser has a definite capacity which may be tuned by means of theinductance coil 17. Accordingly, each one of the piezoelectric crystals68, inclusive, is connected in series with a further resonant circuit,tuned approximately to the same frequency as is the crystal. The Q ofthe piezo-electric crystal may be of the order of 10,000 to 10,000,000,depending upon the structure and mounting of the piezo-electric crystal.On the other hand the measured Q of a specific circuit consisting of aprobe, a layer of electrically conductive plate, and an intermediatephosphor, in series with a tuning coil has been found to beapproximately to 40. Accordingly, the series tuned circuit whichincludes the coil and electroluminescent condenser is relatively low Qand the piezo-electric crystals are each extremely high Q circuits. Itfollows that a large number of crystals may fall substantially withinthe resonance curve of the electroluminescent condenser and its tuningcoil 17 Upon application to the terminal 1 of a signal falling withinthe predetermined band of frequencies, f1 and f2, one of piezo-electriccrystals 6, 7, 8, represents a short circuit to the frequency of thesignal, all the remaining crystals being essentially open circuits. Thesignal passes through the crystal which is conductive and thence throughthe phosphor and the tuning coil to ground. A resonant rise of voltageoccurs across the condenser, and the phosphor which subsists immediatelyunder the activated one of contacts 10, 11, 12, glows. shunt capacity ofthe remaining crystals, or which occurs at frequencies harmonicallyrelated to those desired, produces no response in the phosphor, unlessthey are of extremely high amplitude, because the phosphor possesses afiring threshold, and does not glow in response to any voltage lowerthan its required firing voltage. This firing voltage is a function ofthe constitution of the phosphor, the constitution of its medium, ifany, and the thickness of the layer of phosphor. Firing voltages havingvalues of volts R. M. S. have been observed, at frequencies 1 of severalmc., and luminous efiects have been observed in electroluminescentphosphors of the general type described in the Mager patent atfrequencies as high as mc./s. and as low as 10 C. P. S.

While I have described and illustrated one specific example of thepresent invention it will be clear that variations of the specificdetails of construction may be resorted to without departing from thetrue spirit of the invention as defined in the appended claims.

What I claim is:

1. A frequency sensitive visual indicator, including a thin layer ofelectroluminescent phosphor material, said layer having a highelectrical resistance in the direction of its thickness, a firstelectrically conductive electrode in contact with one side of saidlayer, a further plurality of electrically conductive electrodes incontact with discrete points of the other side of said layer, which areopposed to said first electrode, a plurality of piezoelectric crystals,each resonant to a different frequency in a frequency band, meansconnecting each of said piezo-electric crystals in series with one ofsaid further plurality of electrically conductive electrodes, means forsupplying signals within said frequency band to said piezo-electriccrystals in Any signal which leaks through the associated parallel, andmeans for tuning the condensers formed by said further conductiveelectrodes and said first electrically conductive electrode to seriesresonance over said frequency band.

2. The combination in accordance with claim 1, wherein said means fortuning is an inductance.

3. A frequency sensitive visual indicator, including a thin layer ofmaterial including electroluminescent phosphor, said layer having highelectrical resistance in the direction of its thickness, a pair ofconductive electrodes on opposite sides of said layer, a piezo-electriccrystal filter in series with one of said pair of electrodes, and meansfor tuning the condenser formed by said electrodes and said phosphor toa frequency equal to one response frequency of said piezo-electriccrystal filter.

4. A frequency sensitive visual indicator, including a thin layer ofmaterial including electroluminescent phosphor, said layer having highelectrical resistance in the direction of its thickness, a pair ofconductive electrodes on opposite sides of said layer, a band-passfilter in series with said pair of electrodes, and means for seriestuning the condenser formed by said electrodes and said layer ofmaterial to a frequency equal to a response frequency of said filter.

5. The combination in accordance with claim 4 wherein said means forseries tuning is a coil in series with said pair of electrodes.

6. A frequency indicating system including an electroluminescentcondenser, a band-pass filter in series with said electroluminescentcondenser, and means for series tuning said electroluminescent condenserto resonate over the band-pass of said filter.

7. The combination in accordance with claim 6 wherein said means forseries tuning is a coil.

8. A frequency indicating system including a plurality ofelectroluminescent condensers, a relatively narrow band-pass filter inseries with each of said electroluminescent condensers, each of saidfilters tuned to a different mean frequency, and a single tuning elementfor simultaneously tuning all said condensers broadly to all thefrequencies passed by said filters.

9. The combination in accordance with claim 8 wherein said means fortuning is a single coil.

10. A frequency indicating system including an electroluminescentcondenser, a band-pass filter in series with said electroluminescentcondenser, and means for tuning said electroluminescent condenser toresonate in the bandpass range of said filter.

11. A frequency sensitive visual indicator, including a thin layer ofmaterial including electroluminescent phosphor, said layer having highelectrical resistance in the direction of its thickness, a pair ofconductive electrodes on opposite sides of said layer, a band-passfilter in series with one of said pair of electrodes, and means fortuning the condenser formed by said electrodes and said phosphor to afrequency in the band-pass range of said filter.

References Cited in the file of this patent UNITED STATES PATENTS1,814,399 Meissner July 14, 1931 2,556,586 Johnson June 12, 19512,624,857 Mager Jan. 6, 1953 2,698,915 Piper Jan. 4, 1955

